Biological nitrogen fixation in soybean in Argentina: relationships with crop, soil, and meteorological factors

Abstract

Aims: This study aims to (i) asses the contribution of biological N fixation (%Ndfa) in the soybean production area of Argentina, (ii) build a model for predicting %Ndfa using crop, soil, and meteorological variables, and (iii) estimate %Ndfa at the country level using values obtained in this study. Methods: %Ndfa was assessed in paddocks and experimental plots located in an area 22–39° S and 56–66° W. %Ndfa was determined using the natural 15N abundance method. A complete data set of soil and meteorological variables (n–47) was used to develop a model for predicting %Ndfa. Results: A median value of %Ndfa in aboveground biomass of 60 % (interquartile range 46–71 %) was estimated. Larger %Ndfa values were observed in areas with high crops yields. When seed yield was above 3.7 Mg ha−1, effective rainfall during fallow and mean temperature in the seed-filling period explained %Ndfa. Below 3.7 Mg ha−1, soil phosphorus content, pH, and effective rainfall in the vegetative period explicated %Ndfa. Conclusions: Soybean production systems in Argentina showed larger %Ndfa than reported values in literature that may affect global N balances. Identified soil and meteorological variables may be useful for predicting %Ndfa in future studies, taking into account their spatial variation in the soil-plant system.